pulsed and square wave voltammetry. digital voltammetry waveforms – staircase used to approximate...
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Pulsed and square wave voltammetry
Digital voltammetry waveforms – staircase used to approximate a ramp for LSV;All modern potentiostats use this approach, also easy to use other input waveforms
All sorts of pulsed voltammetry methods were developed in 1950-60s by Sir Geoffrey Barker in UK, and later 1970-80s modernized by Janet and BobOsteryoung in the US
Etime
Basis of all pulsed methods: Response of reversible system to a potential pulse;Measuemenst at end of pulse discriminates against charging current
I
Faradaic
Charging (decays faster)
60 ms
measurement
Idl (E /Rs)exp{ t /CdRs}
IF nFAD o
1/ 2Co*
(t)1/ 2(1 )
exp[nF /RT(E E o ')]
Normal Pulsed Voltammetry (simplest) DL about 15-fold lower than cyclic voltammetry (CV)
Input waveform
output
Input waveforms output
Ep
Differential Pulse voltammetry
Normal pulse voltammetry
nM detection limits
Ep
Square Wave Voltammetry – complex waveform, derivative output most sensitive instrumental electrochemical method
Input waveform
outputnM detection limits;Slightly better thanDifferential pulse
SWV outputs
Net or difference current
Reverse current
Forward Current
NPV SWV
O1 + e == R1
R1 + e == R2
Better resolution, Best sensitivity
I x 1000
difference current
forward
reverse
Net or difference current
SWV Output
SWV parameters - increasing frequency (effect of DE is similar)
Approx DL
NPV
DPV
SCV or LSV(CV)
SWV
10-6 M/n
2x10-9 M/n
5x10-5 M/n
10-9 M/n